The microscopic screening of cytologic samples is a tedious, time-consuming, repetitious task that technicians are often required to perform a hundred or more times every working day.
All tissues are composed of cells, the cell being the basic living unit of animal and plant matter. Many body organs are composed of or lined by epithelial tissue. As a result of continuous growth and replacement the most superficial cells of an epithelium are constantly shed and replaced by younger cells in a form of spontaneous exfoliation. Exfoliated cells are found in body fluids such as secretions from the female genital tract, gastric fluid, urine, cerebrospinal fluids, punctates exprimates or washings from epithelial surfaces. These exfoliated cells can be collected from certain body sites for microscopic examination. In addition, spontaneously exfoliated cells can be supplemented by cells obtained directly from certain organs by use of suitable instruments. Such cells can be employed for detection and diagnosis of various pathological conditions.
Automation of this task would speed up the identification of abnormal cells, eliminate the problem of human fatigue associated with microscopic analysis and tend to reduce the overall cost of such analysis. Identification of single abnormal cells is at the core of any successful automation procedure. In order to achieve this goal it is necessary to prepare isolated single cells for flow-through type counters or a specimen approximating a cell monolayer for microscopic analysis. Techniques already exist for the identification of the complete spectrum of gynecologic cells in a clean specimen of isolated cells. However, techniques do not exist at the present for the adequate preparation of a specimen which constitutes a suspension of isolated single cells without cell overlap, cell aggregation, cell loss, or cell damage. Overlapping cell nuclei, groups of closely-packed polymorphonuclear leucocytes, and dark cytoplasmic areas are frequently incorrectly interpreted by automatic or semi-automatic machine screening as large, dark "malignant" nuclei. Once a proper suspension has been achieved, problems specific to automated flow-through systems or for automated slide base systems are within the capabilities of present technology.
The detection of carcinoma in the female genital tract is a prime example of the use of diagnostic cytology or human cell interpretation. Exfoliated cells which accumulate in the vagina together with cells scraped from the uterine cervix provide the cytopathologist with information for detecting carcinoma with a high rate of reliability. Cytologic material presently collected from the vagina or uterine cervix and/or uterine cavity by a physician or trained paramedic personnel is smeared on glass slides and fixed to preserve morphologic and chemical structure. Samples are sent to the cytology laboratory in which they undergo an elaborate staining procedure, such as Papanicolaou stain. After staining, the slides are scanned under a microscope by cytotechnicians trained to identify normal and abnormal cells. Since the great majority of smears can be expected to be normal, it is apparent that some sort of automatic apparatus would be of significant value in screening out all obviously normal smears, leaving questionable and abnormal ones for further examination by cytotechnicians and pathologists.
Various automatic apparatus have been built to monitor cells based chiefly on differences in cell area or size along with total cell radiation, absorption or cell optical density. The reliability of such apparatus has proved to be extremely poor when separating the spectrum of cells under consideration.
The single most significant problem in preparing specimens has been the clumping of cells which makes it impossible for a machine to discriminate between the signal originating, for example, from a single cancer cell and the signal resulting from a cluster of benign cells which electronically could have similar parameters. This problem has not been obviated by the various attempts at automation which have been introduced in recent years, including agitation, homogenation, syringing, force filtration, ultrasonics, shaking, stirring, and the like to achieve dispersal of cell aggregates. Such cell aggregates, often composed of only two or three cells, have persisted as the major obstacle to full automation, since they can be particularly misleading to automated equipment. In contrast, the human counterpart has little difficulty in supressing extraneous visual information and cytologists can read slides containing tissue fragments, overlapping cells, and the like.
The difficulty with efforts to artificially or chemically disrupt cells has been the extensive damage which normally occurs during such attempts. Some mechanical methods, for example, tear cells apart and can also rip away parts of cell membranes and cytoplasm. The insuing cellular damage can make the specimen unacceptable for automatic analysis, since the cells are destroyed and automated equipment cannot contend with the resulting debris. Ultrasonic dispersion in particular tends to be too violent to be used as a method for cell dispersal. It frequently results in extensive cell damage, with the production of cytoplasmic fragments. Treatment with a homogenizer, such a household or laboratory blender, e.g., a Waring blender, produces an especially violent result, tending to cause extensive cell damage and destruction.
Syringing is one of the simplest methods of dispersing cells, but syringing has to be performed very carefully in order to achieve the desired result. Little success has been achieved with forced filtration. Apparently, the shearing forces are of insufficient strength and are applied for insufficient time to break down the cellular attachments. Rapid shaking, as with a Vortex mixer, readily disperses cell clumps, but has little or no effect on tissue fragments.
Attempts have also been made to chemically separate cell clusters. Analysis of the cell junction in cervical samples tends to suggest that desmones bind endocervical normal and malignant cells in situ. Desmones are ubiquitous cell juntions. It is extremely difficult to separate cells by disrupting desmones without destruction of the cell membrane. Consequently, most chemical approaches have failed because attacks on the cell juntion also resulted in destroying the cell membranes themselves.